shallow and deep scan modes

#### Modes :
- `--shallow` : fast but prone to errors
- `--deep` : slow but accurate

Look at the existing scanning logic in the codebase to understand how dependencies are currently detected. Determine what constitutes a 'shallow' vs 'deep' scan—likely scanning fewer files or using faster heuristics versus a comprehensive analysis. Implement the command-line flags and the corresponding scanning modes, ensuring they integrate with the main entry point. Test both modes on sample projects to verify the speed/accuracy trade-off.

索引モデルが issue の本文から書いたものです。